Security for doors has become an increasing problem especially for certain types of businesses, such as office buildings and hotels where the occupancy of a particular secured room changes frequently requiring either installation of new locks or rekeying of existing locks in order to provide a completely secured door. Otherwise, if left unattended it would enable unauthorized previous users of the premises to gain access through the door easily by use of a previously owned key or duplicate thereof. In order to eliminate such problems, various types of security locks have been devised which incorporate various types of electronic devices which can be programmed for rapid change of an access code. However, these prior art electronic locks require holes to be cut into the door, mounting plates attached, installation of wiring and other time consuming and costly adaptations in order to incorporate them into an existing lockset. It is desirable for such electronic locks that the lock can be used both electronically with a code and/or mechanically with a key or a combination of both. In known electronic locks using batteries as the power source for the electronic components, problems occur in that, when the batteries become low a warning light or signal is usually emitted to enable the occupant to change batteries. However, should the lock go unattended in this low power condition and the batteries lose sufficient power for operation of the lock, the occupant could be locked out of the premises since the lock becomes inoperative until the batteries are replaced. It is also undesirable for the occupant to hurry and replace batteries at inconvenient times. Another known problem with existing electronic locks using a battery source is that the battery is used as the power source to drive a motor for moving the locking bolt and, therfore, uses a susbstantial amount of power which reduces the life of the battery.
The most pertinent known prior art electronic locks to our invention are shown in U.S. Pat. Nos. 1,695,518; 3,494,157; 3,670,538; 3,764,859; 3,787,812; 3,894,417; 4,393,672 and 4,458,512. However, all of these prior devices require special modifications to an existing door lockset, or require a completely new lock to be installed in the door and associated doorframe. None of these devices discloses an electromechanical locking device which is self-contained within a doorknob which is easily retrofitted on an existing lockset by removing one of the existing doorknobs and slideably inserting the doorknob on the existing lockset without any further modifications to the lockset or surrounding locking hardware. Other known prior art locking devices and security systems using electronic components, individually or in combination with a mechanical locking device, are shown in the following U.S. Pat. Nos. 3,134,254; 3,392,558; 3,392,559; 3,408,838; 3,411,046; 3,415,087; RE 27,013; 3,733,862; 3,845,362; 3,926,0212; 4,200,227; 4,209,782; 4,250,533; 4,286,305; 4,507,944; 4,519,228; 4,534,194., 4,548,061; 4,565,080; 4,616,491 and 4,626,848.